The invention relates to a method for installing a duct in the ground, whereby a longitudinal organ is already present in the ground near the route along which the duct is to be installed, whereby the existing longitudinal element is used as a guide for the duct to be installed and the duct is pushed into the ground with the aid of a fluid under pressure fed through the duct.
Such a method is known from U.S. Pat. No. 5,639,183. The known method is intended to replace an existing telecom cable, in particular a copper cable, by installing a duct through which an optical cable can be fed. With this method the existing cable is dug free at a suitable point and cut through. The duct is then pushed over an end that has been freed in this way. In order to install the duct around the existing cable over a greater length in the ground, a liquid, for example water, is fed under pressure via the duct, to the free end thereof, which flushes away the ground around the existing cable, while at the same time the duct is pushed forwards. In this way a duct, or a duct consisting of a plurality of coupled segments, can be installed over a large distance in the ground over an existing cable without the need for much digging. After the installation, the cable can, if desired, be pulled out of the duct.
The known method is particularly suitable for replacing existing copper telecommunication cable by a cable-duct in which optical fibre cable can be installed in order, for example, to install optical fibre right up to the user, i.e. up to the dwelling or the business. The optical fibre cable can, for example, be installed in the duct by means of blowing or pulling, with installation by means of blowing being preferred, since the forces exerted on the optical fibre cable by this method are distributed over the whole length, thus avoiding damage due to excessive tensile forces. Such a method for blowing in a cable is described in EP-A-0 292 037. In addition, a combination of blowing and pulling is possible by attaching a so-called shuttle to the end of the optical fibre cable.
In some situations it is undesirable to cut the existing cable in order to be able to push the duct over it. This is, for example, the case if the cable must remain available for other purposes, for example for use by another provider of telecommunication services. It is an object of the present invention to provide a solution for this problem. To this end, the invention provides a method for performing the above-mentioned procedure, whereby the duct to be installed is coupled by at least one divisible coupling piece to the existing longitudinal element and whereby the coupling element is advanced along the existing longitudinal element.
The invention is based on the understanding that it is possible, without interrupting the longitudinal element already present in the ground, nevertheless to use this element as a guide for installing a new duct. The longitudinal element will in many cases be a telecommunication cable or a cable suitable for other purposes, but an existing gas or water pipe, for example, can also be used as a guide. The duct will in most cases be a cable-duct, but the invention may also be used advantageously to install other ducts, such as for example flexible water or gas pipes.
The invention further provides a device for installing a duct under the ground in the vicinity of an existing longitudinal element comprising: a divisible coupling piece provided with means to attach the coupling piece movably along the longitudinal element and means to connect the duct immovably to one end of the coupling element, as well as means to allow a fluid fed through the duct to flow out via the other, opposite, end.
If the tubular organ needs to be installed over great distances, it may be desirable for the duct being installed to be coupled at intervals to the existing longitudinal element. To this end, the invention provides coupling means which are similar to the coupling means described above, but are provided with a coupling channel for the duct being installed, running from one end to the other end, and whereby there should be no nozzle for the fluid.
The fluid used for the installation can, as in the known method, be a liquid such as water, but can also be a gas, such as air. In many cases, the installation of the duct will not require the use of a relatively complex above-ground installation, such as described in the above-mentioned U.S. Pat. No. 5,639,183, but a simple pump to feed liquid or gas under pressure to the inlet opening of the duct being installed will be sufficient and enable the duct to be inserted by manual effort.